The Registry Set concept was invented by numismatic marketing genius David Hall, (who also co-founded PCGS.) Collectors can display their Registry Sets online, which creates highly competitive atmosphere. Because the coins must be in the proper company's holder to qualify, many coins are graded that might not otherwise be (especially post-1960 coins.) Market prices for these coins are also driven by Registry Set competition, resulting in crazy prices for extremely common coins, late-date coins that are in high grades.
Can a Coin With a Mintage of 3,300,000,000 be Rare?
Learn the Difference Between Mintage Rarities and Grade Rarities.